1. Field of the Invention
The present invention relates to a display device in which a thin film transistor is used at least in a pixel portion.
2. Description of the Related Art
In recent years, technology that is used to form thin film transistors using semiconductor thin films (with thicknesses of from several tens of nanometers to several hundreds of nanometers, approximately) formed over substrates having an insulating surface, for channel formation regions, has been attracting attention. Thin film transistors are applied to a wide range of electronic devices such as ICs or electro-optical devices, and prompt development of thin film transistors that are to be used as switching elements in image display devices, in particular, is being pushed.
As a switching element in an image display device, a thin film transistor in which an amorphous semiconductor film is used for a channel formation region, a thin film transistor in which a polycrystalline semiconductor film is used for a channel formation region, or the like is used.
As a switching element in an image display device, further, a thin film transistor in which a microcrystalline semiconductor film is used for a channel formation region is used (see Reference 1: Japanese Published Patent Application No. H4-242724; and Reference 2: Japanese Published Patent Application No. 2005-49832).